Various methods for the separation and recovery of proteins, nucleic acids or their fragments are carried out by electrophoresis for the preparation of recombinant DNA, the cloning of DNA, the preparation of antibodies, the determination of amino acid sequences, the mapping of peptides and the analysis of amino acids. For instance, a method of electrical elution which comprises excising the gel containing the substances separated by electrophoresis and re-exposing the gel thus excised to an electrical field to elute the substances from the gel, a blotching method which comprises superimposing a filter paper or a nitrocellulose film on the gel containing the substances to be separated to transfer them to the carrier, a gel structuring method which comprises crushing and pulverizing to extract the substances to be separated, and a gel dissolution method which comprises decomposing the crosslinks of the gel by a chemical reaction to elute off the substances in the gel, having been developed. However, these methods have been said to be disadvantageous in that numerous complicated recovery steps are required, the recovery rate is low and the sample is denatured. Particularly fatal is the low recovery rate when such methods are used to separate and recover trace amounts of proteins or nucleic acids.
On the other hand, solubilizable gels have been developed for the purpose of achieving a high recovery yield. When N,N'-methylenebisacrylamide is employed as the conventional crosslinking agent, the polyacrylamide gel thus obtained has to be solubilized under a comparatively severe condition as in an aqueous 30% (w/v) hydrogen peroxide solution at 50.degree. C. However, the solubilizable gels can be dissolved in an aqueous solution under a comparatively mild condition. Typical gels are ones which can be obtained by crosslinking the polyacrylamides with a decomposable crosslinking agent such as N,N'-diallyltartardiamide, N,N'-(1,2-dihydroxyethylene)bisacrylamide, N,N'-bisacrylcystamine and ethylene diacrylate. A method which comprises separating substances by electrophoresis using the above described gel, excising each portion containing said substances, respectively, and solubilizing the excised portions of the gel by oxidation, reduction or hydrolysis to elute the substances in the gel, has been developed. However, the problem with this method is that the separated proteins or nucleic acids have to be re-separated from the solubilized gel. Particularly at the time when the gel is solubilized, even if 100% recovery yield is possible, the yield of recovery may be disadvantageously decreased in the later step of the separation from the solubilized gel [for example, see D. C. Flter and S. S. Tevethia: Virology, 117:267-270 (1982)].
Thus, even when the conventional method is employed for the separation of substances by electrophoresis, it is very difficult to recover the substances from the gel by a simple method and at a high recovery yield.